The changing fractions of type IA supernova NUV–optical subclasses with Redshift

Journal Article · Fri Apr 10 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/803/1/20· OSTI ID:22882570

Milne, Peter A. ^[1]; Foley, Ryan J. ^[2]; Brown, Peter J. ^[3]; Narayan, Gautham ^[4]

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1. University of Arizona, Steward Observatory, 933 N. Cherry Ave., Tucson, AZ 85719 (United States)
2. Astronomy Department, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)
3. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A. and M. University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843 (United States)
4. National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States)

Ultraviolet (UV) and optical photometry of Type Ia supernovae (SNe Ia) at low redshift have revealed the existence of two distinct color groups, composed of NUV-red and NUV-blue events. The color curves differ primarily by an offset, with the NUV-blue u−v color curves bluer than the NUV-red curves by 0.4 mag. For a sample of 23 low-redshift SNe Ia observed with Swift, the NUV-red group dominates by a ratio of 2:1. We compare rest-frame UV/optical spectrophotometry of intermediate- and high-redshift SNe Ia with UVOT photometry and Hubble Space Telescope spectrophotometry of low-redshift SNe Ia, finding that the same two color groups exist at higher redshift, but with the NUV-blue events as the dominant group. Within each red/blue group, we do not detect any offset in color for different redshifts, providing insight into how SN Ia UV emission evolves with redshift. Through spectral comparisons of SNe Ia with similar peak width and phase, we explore the wavelength range that produces the UV/optical color differences. We show that the ejecta velocity of NUV-red supernovae (SNe) is larger than that of NUV-blue objects by roughly 12% on average. This velocity difference can explain some of the UV/optical color difference, but differences in the strengths of spectral features seen in mean spectra require additional explanation. Because of the slightly different b−v colors for these groups, NUV-red SNe will have their extinction underestimated using common techniques. This, in turn, leads to underestimation of the optical luminosity of the NUV-blue SNe Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.

• OSTI ID: 22882570
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 803; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
DISTANCE
EMISSION
LUMINOSITY
NEAR ULTRAVIOLET RADIATION
PHOTOMETRY
RED SHIFT
SPACE
SPECTRA
SPECTROPHOTOMETRY
TYPE I SUPERNOVAE
VELOCITY